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Magnetism
Analogy in Magnetism & Electrostatics There is an analogy between permittivity and permeability of free space in electrostatics and magnetism . Revolving Electron The ratio of magnetic dipole moment with angular momentum of revolving electron is called as gyromagnetic ratio . Gyromagnetic Ratio = M/L = 8.8 x 1010 C / kg magnetic moment = m = evr / 2 Magnetization The net magnetic dipole moment per unit volume is called as Magnetization (Mz) . Mz = Mnet / Volume Also , Mz = C x Bext / T Consider a torroid with iron core on it . As current flows through the torroid it sets up a magnetic field around itself . This magnetic fild now magnetizes the iron core . Magnetic Field due to torroid Bo = μonI Magnetc Field due to iron core BM = μoMz Now , B = B0 + Bm ..... B = μonI + μoMz Magnetic Intensity Magnetic Intensity (H) is a quantity used in describing magnetic field strength of a field . It is defined as follows : B0 = μoH = μonI ; i.e. H = nI Now , B = μonI + μoMz B = μoH + μoMz B = μo(H + Mz) Susceptibility The relation between magnetization(Mz) and intensity(H) is given as : Mz = XH ; where X is the magnetic susceptibility of the substance (iron core in example) Now , B = μo(H + Mz) = B = μo(H + XH) B = μo(1+X)H B = μoμrH μ = μ0μr = μo(1+X) Domain Theory The region in which all the magnetic moments are aligned in the same direction are known as domains . Diamagnetism Silver , lead , silicon , nitrogen , sodium chloride , copper , antimony , gold , mercury , water , air , hydrogen , etc. 1) All the orbitals are completely filled . 2) The spins are paired and the magnetic field is repelled . The diamagnetic materials move away from stronger magnetic field to weaker magnetic field . 3) If a thin rod of diamagnetic substance is freely suspended in external magnetic field , it comes to rest with it's length perpendicular to the field . 4) In absence of external magnetic field , the net magnetic moment is zero . Paramagnetism Aluminium , Manganese , Chromium , Platinum , oxygen , sodium , calcium , lithium , copper chloride , tungsten , niobium , etc. 1) Atom contains unpaired electron ; i.e. their orbitals are not completely filled . 2) The spins do not cancel each other and the magnetic field is attracted . The paramagnetic materials move towards the stronger magnetic field . 3) If a thin rod of paramagnetic substance is suspended freely in a magnetic field , it comes to rest , parallel to the magnetic field . 4) In absence of external magnetic field , the dipole moments of atoms are randomly oriented , and hence the net dipole moment is zero . Ferromagnetism Iron , Nickel , Cobalt , gadolinium , dysprosium and their alloys , etc. 1) Atom contains a large number of unpaired electrons , which results in large magnetic moment . 2) The ferromagnetic materials move towards the stronger magnetic field . 3) When ferromagnetic substances are kept in magnetic field , they get strongly magnetized in the direction of magnetic field . 4) In the absence of external magnetic field , these materials have a resultant magnetic moment . Curie Temperature The temperature at which the domain structure is destroyed and the ferromagnetic substance loses its magnetism , is called Curie Temperature . Above Curie temperature , ferromagnetic substances become paramagnetic . Category:Physics